Fig. 1.

Balance between oxidative stress and self-defense systems determines whether the cell/tissue/organ condition is pathological or healthy.

Self-defense systems, such as antioxidant systems that remove ROS and alleviate oxidative stress, and repair systems that aid recovery from the resulting disorders, are present in vivo. If the accumulated ROS and oxidative stress exceed the capacity of the antioxidant and/or repair systems, cell/tissue/organ disorders and death ensue and may cause disease pathogenesis, although as long as the capacity of the antioxidant and repair systems is retained, the cells, tissues, and organs remain healthy. ROS, reactive oxygen species.